Knee prosthesis

ABSTRACT

A knee joint prosthesis comprises a femoral component having a pair of laterally spaced-apart condylar portions received on the femoral condyles and having surfaces shaped substantially to match the shapes of the condylar surfaces of the femur and an intercondylar portion connecting the femoral components together. The intercondylar portion has a medial slot that opens toward the tibial plateau. A tibial component in the form of a generally plate-like platform is placed on the tibial plateau and has laterally spaced-apart tibial surfaces disposed opposite from and supporting the condylar surfaces of the femoral component. A post extends upwardly from the tibial component into the slot in the femoral component, and an axle extends transversely through openings in the post and the intercondylar portion of the femoral component to connect the tibial and femoral components together in hinged relation for relative pivotal movement of the components about a transverse pivot axis to afford flexion of the leg.

United States Patent 1191 Walker 1451 Sept. 24, 1974 I KNEE PROSTHESIS [75] Inventor: Peter S. Walker, New York, NY.

[73] Assignee: New York Society for the Relief of the Ruptured and Crippled, New York, NY.

[22] Filed: Dec. 7, 1972 [21] Appl. No.: 312,850

[52] US. Cl. 3/1, 128/92 C [51] Int. Cl. A61f 1/24 [58] Field of Search..... 3/1; 128/92 R, 92 C, 92 CA [56] References Cited UNITED STATES PATENTS 3,696,446 10/1972 Bousquet et al. 3/1 3,715,763 2/1973 Link 3/1 3,728,742 4/1973 Averill et al. 3/] 3,748,662 7/1973 Helfet 3/1 3,765,033 10/1973 Goldberg et al. 3/1 OTHER PUBLICATIONS Vitallium Surgical Appliance Catalog, Austenal Medical Division, Howmet Corp., New York, N.Y., 1964, M.G.H. Femoral Condyle Replacement (No. 6662), page 62.

Primary Examiner-Richard A. Gaudet Assistant Examiner-Ronald L. Frinks Attorney, Agent, or FirmBrumbaugh, Graves, Donohue & Raymond [5 7] ABSTRACT A knee joint prosthesis comprises a femoral component having a pair of laterally spaced-apart condylar portions received on the femoral condyles and having surfaces shaped substantially to match the shapes of the condylar surfaces of the femur and an intercondylar portion connecting the femoral components together. The intercondylar portion has a medial slot that opens toward the tibial plateau. A tibial component in the form of a generally plate-like platform is placed on the tibial plateau and has laterally spacedapart tibial surfaces disposed opposite from and supporting the condylar surfaces of the femoral component. A post extends upwardly from the tibial component into the slot in the femoral component, and an axle extends transversely through openings in the post and the intercondylar portion of the femoral component to connect the tibial and femoral components together in hinged relation for relative pivotal movement of the components about a transverse pivot axis to afford flexion of the leg.

19 Claims, 6 Drawing Figures PATIENTEDSEPZMQM S EU of 2 I FIG. 2

KNEE pnosrnnsrs BACKGROUND OF THE INVENTION The knee joint is the largest joint of the body, is subject to the greatest stress of any joint in the body and is required to sustain the high stresses while permitting not only flexural movement of the leg in a posterioranterior direction but a significant amount of relative rotation or swivelling between the femur and the tibia about the axis of the tibia (or the axis of the femur, depending upon what the leg is doing or ones point of view) an anterior-posterior relative translation between the femur and tibia. Moreover, the bone structure and soft tissue structure associated with it must provide a high degree of stability in various positions. For example, the leg in the extended position involves a locking of the joint against flexure of the leg beyond the normal extended position. Various injuries and diseases of the knee joint are frequently of sufficient severity to partially or totally prevent functioningof the joint and can be extremely painful.

US. Pat. application Ser. No. 224,479, filed Feb. 8, 1972, now U.S. Pat. No. 3,774,244 by the present inventor, for Knee Joint Prosthesis" (assigned to the assignee ofthe present invention) describes and illustrates a knee joint prosthesis that provides for either partial or total replacement of the interengaging surfaces of the femoral and tibial condyles. The prosthesis of that application affords relief from pain and restores function and load-bearing capability to a knee-joint that is, as a result of disease or injury, rendered partially or fully incapable of function, principally as a result of failure of the femoral and tibial condyles but which, nonetheless, retains most of its stability. As described in more detail below, certain features of the knee joint prosthesis described in the aforementioned prior application are, preferably, included in the knee joint prosthesis described and illustrated herein, and reference may be made to that prior application for a complete description of such features.

SUMMARY OF THE lNVENTlON There is provided, in accordance with the present invention, a knee joint prosthesis intended for use in knees that as a result of injury or disease are not only partially or totally incapable of normal function, but have been damaged to the point of being markedly unstable; in other words, not only are the condyles incapable of functioning properly to transfer loads from the femur to the tibia and to afford proper articulation, but other components such as ligaments and other soft tissues of the knee joint have been damaged or destroyed or there has been substantial destruction or erosion of bone so that replacement of the condylar surfaces does not restore function and stability.

More particularly, a knee joint prosthesis, according to the present invention, includes a femoral component having a pair of laterally spaced-apart condylar portions placed at the femoral condyles and a generally U- shaped intercondylar portion that interconnects the femoral components. The cavity or opening between the legs of the U opens generally toward the tibia and posteriorally and provides a slot in the intercondylar portion of the femoral component. A tibial component in the form of a plate-like platform having laterally spaced-apart femoral surfaces at the lateral portions of LII its outwardly facing surfaces opposite the femoral condylar portions of the femoral component is placed on the tibial plateau. A post extends upwardly from the medial portion of the upper surface of the tibial component and into the slot between the legs of the U-shaped intercondylar portion of the femoral component. An axle extends through holes in the post of the tibial component and the legs of the intercondylar portion of the femoral component and couples the tibial and femoral components to each other in hinged relation for relative pivotal movement of the components about a transverse pivot axis, thereby to afford flexion of the leg.

A' preferred form of prosthesis according to the present invention embodies femoral and tibial condylar portions of the femoral and tibial components that are shaped in the manner described in the prior application of the present inventor referred to above, and reference may be made to that application for a full description and illustration of the condylar surfaces of the two components. Briefly, however, the femoral condylar portions are anteriorally posteriorally elongated, doubly curved, plate-like members having a varying curvature in the anterior-posterior direction that conforms generally to the anterior-posterior anatomical shape of the femoral condyles. The condylar surface of each femoral condylar portion is of uniform transverse shape throughout its length and includes a substantially flat portion at the laterally outward portion and convexly curved portions at the laterally inward portions. Each condylar surface of the tibial component is a surface generated by moving an anteriorally posteriorally oriented line along a path conforming to the transverse shape of the corresponding condylar surface of the femoral component. In other words, in transverse cross section, each tibial condylar surface has a shape matching the transverse shape of the femoral condylar portion of the femoral component and is essentially uniform in all transverse sections along its anteriorposterior length. The matching transverse curvatures of the intereng'aging condylar surfaces of the two components of the prosthesis provide lateral stability in the joint in that they restrict relative lateral displacement between the components, but articulation of the joint in a manner closely resembling the normal anatomical articulation or flexure of the joint is provided.

The condylar surfaces-of the tibial component (that is, those surfaces of the tibial component that are engaged by the femoral component) are preferably-generated by straight lines and thus are straight in all lateral cross-sections taken in anteriorally posteriorally extending planes. Accordingly, anterior-posterior displacement of the femoral component relative to the tibial component, a function that is afforded by the anatomical knee joint, is permitted by the prosthesis.

The hinge connection between the femoral and tibial component of the prosthesis of the present invention provides enhanced stability of the knee joint, as compared with the prosthesis described and illustrated in the prior application referred to above. Nonetheless, the form of the prosthesis of the present invention provides flexibility or laxity closely resembling that of the anatomical knee joint, thereby facilitating an approximation of normal knee joint function. In particular, rotational laxity, that is, the ability of the tibia to rotate about its longitudinal axis relative to the femur is afforded by providing the following geometrical and dimensional characteristics:

1. a predetermined clearance between the axle and the hole in the intercondylar portion of the femoral component in which the axle is received;

2. predetermined clearances between the lateral surfaces of the post of the tibial component and the faces of the slot in the intercondylar portion of the femoral component which receives the post, and

3. the cross-sectional shapes of the slot and post are so related as to afford limited pivoting of the post in the slot.

Preferably, the clearance between the axle and the hole through which it passes varies, depending upon the degree of flexure of the knee, the degree of rotational laxity increasing from a relatively small amount of a few degrees of relative rotation when the leg is extended to a somewhat larger degree of rotation, say, somewhere on the order of 9 to of relative rotation, when the leg is substantially flexed. The clearance between the axle and the hole or holes through which it passes in the hinge connection and the lateral clearances between the lateral faces of the post and the faces of the slot allow the desired amount of relative rotation of the prosthesis components but restrict rotation beyond the desired value.

In a preferred form, the post of the tibial component has, in cross section (in planes generally perpendicular to the longitudinal axis of the tibia) lateral surfaces that converge outwardly, relative to a plane passing through the axis of the axle and substantially perpendicular to the principal plane of the outwardly facing surface of the tibial component. Such convergence may be either in the form of convexly curved lateral surfaces or flat, convergent faces.

The clearance relationships described above (and described in more detail below) permit the prosthesis to function in a manner closely approximating normal anatomical function. Preferably, however, inasmuch as flexibility in the joint is somewhat inconsistent with stability, the flexibility provided by the geometry of the prosthesis and, in particular, by the various clearances intentionally provided to produce the desired flexibility, is somewhat less than that provided by the anatomical knee joint. In any case, the degree of flexibility is a matter of the precise design of the prosthesis and can be varied in accordance with the opinions of the doctors in the circumstances of a particular patient or type of patient.

The components of the prosthesis are implanted in the knee joint in assembled relation, thus facilitating the surgical procedure and ensuring accuracy of location of the parts relative to one another, and are secured by an appropriate cement, such as a cement based on polymethyl methacrylate. Firm fixation of the femoral component in the femur is enhanced by providing, in the femoral component, a pin that extends through the epiphysis of the femur, preferably within the cortex, and a short distance into the lower portion of the femoral diaphysis. Some bone removal on the epiphysis is necessary to accommodate the intercondylar portion of the femoral component and a small amount of resecting of the femoral condyles in regions that will underlie the femoral condylar portions of the femoral component of the prosthesis may be appropriate. In addition,'the internal surfaces of the femoral condylar portions of the femoral component may be provided with a series of small. bosses or pins that project into a body of cement installed in the resected portions of the femoral condyles.

The tibial component is implaced on the tibial plateau, also using an appropriate cement for securement, by resecting a small amount of the cortex of the tibial epiphysis in the region that will underlie the tibial component. Fixation of the tibial component is enhanced by providing undercut or dovetail-shaped grooves in the undersurface of the tibial component and providing ribs or flns that depend downwardly and extend some distance into the tibia. A pin is installed through a hole through the anterior portion of the tibial component, the pin extending through the tibial epiphysis within the cortex and into the upper end of the tibial diaphysis and being cemented in place.

Although various materials may be used for the prosthesis, it is preferable to employ a surgical metal, such as a surgical cobalt-chrome alloy. The interengaging surfaces of the components should be highly polished to reduce friction to a minimum and to minimize wear and thus prolong useful life.

A knee joint prosthesis, in accordance with the present invention, provides various important advantages. The fact that the two components are physically interconnected and are geometrically and dimensionally formed to restrict relative movements other than those intentionally provided to accommodate anatomical knee function ensures stability of a corrected joint in which the prosthesis is implaced. Thus, the ability to restore stability to an unstable anatomical knee joint is, of course, the most important advantage of this invention. The prosthesis also permits limited relative movements, thus retaining the laxity of the anatomical knee joint and providing restoration of function approximating anatomical function. The laxity afforded by the prosthesis also reduces the forces imposed on the fixation sothat loosening is less likely to occur. The prosthesis requires a minimum amount of bone cutting and resection before placement, and yet the components are securely fixed to the bones and are not likely to require replacement. On the other hand, if there is a failure of the prosthesis, there will still be adequate bone available for another implacement or for an alternate surgical procedure. The components are strong, durable and long wearing, thus making a failure of the prosthesis very unlikely in any case.

DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may be made to the following description of an exemplary embodiment, taken in conjunction with the figures of the accompanying drawings in which:

FIG. 1 is a side view from the external side of a right knee joint having the prosthesis implaced therein, the bones being shown in outline only and the prosthesis being shown in full elevation;

FIG. 2 is a front view, partly in elevation and partly in section, as represented by the lines 2--2 of FIG. 1 and the direction of the arrows, of the prosthesis of FIG. 1;

FIG. 3 is a top view of the tibial component of the prosthesis of FIGS. 1 and 2;'

FIG. 4 is a top view in cross-section of a portion of the prosthesis, the crosssection being taken generally along the lines 44 of FIG. 2 and in the direction of the arrows, and the viewbeing on a larger scale than FIG. 2;

FIG. 5 is a side elevational view showing the axle and the hole in the tibial post on a larger scale than FIG. 1; and

'FIG. 6 is a side view of the external side of the prosthesis (as in FIG. 1) illustrating the prosthesis in the position it assumes with the knee flexed to 90.

DESCRIPTION OF EXEMPLARY EMBODIMENT FIGS. 1, 2 and 6 of the drawings illustrate an exemplary embodiment of the prosthesis, according to the invention, in place at the knee joint of a human leg. The femur (thighbone) l0 and the tibia (legbone) 12 are shown in dotted outline. The prosthesis includes a femoral component 14, a tibial component 16, a tibial pin 18 by which the tibial componentis more firmly secured to the tibia anda hinge pin or axle 20 by which the femoral component and tibial component are connected together for relative pivotal movement to afford flexure of the knee joint.

The femoralcomponent 14 consists ofa pair of laterally spaced-apart femo'ral'condylar portions 22, each of which is a doubly curved, plate-like element having an anterior-posterior curvature and a length generally conforming to the corresponding condylar surface of the femoral condyle and having in transverse cross sections (FIG. 2) along its length, a relatively flat outer portion 24 along the lateral extremities and a curved inner portion 26. Each femoral condylar portion of the femoral component is of generally uniform crosssection throughout its length. Projections in the form of small pins 27 on the internal surfaces of the femoral condylar portions 22 extend into a layer of cement placed in a resected portion of the femoral epiphysis underyling the femoral condylar portions 22 and assist in fixation of the femoral component.

The femoral component further includes a generally U-shaped intercondylar portion 28' that interconnects the femoral condylar portions 22 and defines between laterally spaced-apart legs of the U a slot 30. The slot 30 is open throughout the portion of the femoral component that faces generally towards the tibia in all positions of the leg. (As described below, the slot 30 receives a post on the tibial component and the slot is therefore necessarily open to allow full flexural movement of the joint). A curved femoral pin portion 32 extends from the upper end of the intercondylar portion 28, and the intercondylar portion and -pin portion together thus extend through the femoral epiphysis. preferably within the cortex, and terminate at generally the area where the epiphysis meets the diaphysis of the femur.

The tibial component 16 is a generally flat, plate-like piece having, in plan (see FIG. 3), a shape appropriate to permit it to be mounted on the tibial plateau and having in the lateral portions of the outwardly facing surface laterally concavely curved portions 34 and 36 that receive and support the femoral condylar portions 22 of the femoral component 14 and function, in the prosthesis, as the condylar surfaces of the tibial plateau. In transverse cross-section (see FIG. 2), the condylar surfaces 34 and 36 of the tibial component are shaped to match the transverse shapes of the corresponding femoral condylar portions of the femoral component. In particular, the surfaces 34 and 36 are surfaces generated by moving a straight line along a path conforming to the transverse shape of the outwardly facing surfaces of the femoral condylar portions 22 of the femoral component, such outwardly facing surfaces constituting the condylar surfaces of the femoral component and matching the condylar surfaces of the femur. The configuration of the femoral condylar portions of the femoral component and the femoral surfaces 34 and 36 of the tibial component are substantially the same as those described and illustrated in U.S. Pat. Application Ser. No. 224,479, filed Feb. 8, 1972, for Knee Joint Prosthesis" (referred to above), and reference may be made to that application for a more complete description of the femoral condylar portions of the femoral component and the condylar surfaces of the tibial component of the prosthesis of the present invention.

The tibial component 16 also has an upwardly extending post 38 that is received in the slot 30 of the femoral component. The hinge pin or axle 20 is fixed in holes in the legs of the intercondylar portion 28 of the femoral component and passes through a hole 40 in the post 38 of the tibial component. The tibial pin 18, which has a slight taper, passes through a hole in the anterior portion of the tibial component. An enlarged head 18a on the pin resides in a recess 42 formed in the upper medial anterior portion of the tibial component. Firm fixation of the tibial component to the tibia is further assured by a transversely extending, undercut groove 46 formed under the anterior portion of the undersurface of the tibial component and a pair of laterally spaced, depending ribs or bosses 48. A body of cement placed under the tibial component protrudes into the undercut slot 46 and provides a keyway lock while the ribs 48 extend down into' adhesive-filled slots cut into the bone. The slot 46 and the ribs 48 ensure fixation of the tibial component against rotational or translational shifting of the tibial component on the tibial plateau.

Referring to FIGS. 4 and 5 of the drawings, the clearances provided in the hinge system of the prosthesis are of considerable importance in providing for controlled laxity in the joint, such laxity being necessary to reproduce in the prosthetic joint the capability of movements approximating the movements afforded by the anatomical knee joint. The flexibility or laxity afforded by the prosthesis is a result of several geometrical relationships and predetermined clearances established in the prosthesis, as discussed in the following paragraphs.

The location of the axis of the axle on the femoral component, relative to the condylar surfaces of the femoral component (that is, the outwardly facing surfaces of the femoral condylar portions 22 of the femoral component) is established to provide pivotal movement of the joint in a manner closely simulating the pivotal or flexural movement of the anatomical knee joint. Moreover, the configuration of the opening 40, relative to the axle 20, provides a locking function that restricts flexure of the joint in a direction beyond the normally extended position of the leg. More particularly, the axis AA of the axle 20 is positioned, relative to an imaginary surface SF defined by the extremities of the condylar surfaces of the femoral component such that the distance DA between the axis AA and the imaginary surface SF is at or near a minimum at the posterior extremity PE of the tibial surface ofthe femoral component and is at or near a maximum at the anterior extremity of the surface SF, the dimension DA varying somewhat at various points along the surface SF but, in general, increasing moving from the posterior extremityPE to the anterior extremity AE. With the leg in fully extended position, as illustrated in FIGS.

1 and 2 of the drawings, the axle resides near the top of the opening 40 in the tibial post 38. Controlled rotational laxity in the knee joint is afforded by providing, in the hinge connection between the tibial and femoral components of the prosthesis, for limited rotation of the tibial component relative to the femoral component. The maximum control over the amount of such relative rotation is a result of l) the configuration and relative dimensions of the axle 20 and the axle opening 40 in the post 38 of the tibial component and (2) the geometry and dimensions of the slot 30 in the femoral component and the post 38. FIGS. 4 and 5 of the drawings illustrate the geometrical and dimensional relationships involved.

In the anatomical knee joint, the ability of the tibia to rotate about its longitudinal axis relative to the femur is, in general, at a maximum with the leg at maximum flexion and diminishes to a minimum with the leg fully extended. This anatomical function is simulated in the prosthesis by providing a variable clearance between the axle and the axle opening 40 in the post 38 of the tibial component. As discussed above, the distance between the axis of the axle 20 and an imaginary surface defined by the extremities of the femoral condylar portions 24 of the femoral component increases for approximately a minimum at the posterior extremity of the femoral condylar portion to a near maximum at the anterior extremity. This dimensional relationship requires that the hinge afford movement of the axis of the pin relative to one of the two components of the prosthesis, and this in turn means that there must be a clearance between the axle and the holes that receive it in one of the two components.

In a preferred embodiment of the prosthesis, the axle, which is preferably of circular cross-section, extends into holes bored in the legs of the intercondylar portion of the femoral component and is tightly fitted within such holes against movement. All clearance in the hinge connection is provided in an enlarged hole of a carefully established shape in the post of the tibial component. It is important to point out at this juncture, however, that a reversal of this particular arrangement is entirely possible; that is, the axle can be rigidly connected to the post of the tibial component and received in specially shaped oversized holes in the legs of the femoral component, such modification representing merely a reversal of parts but no essential difference in function. Assuming, merely for purposes of simplifying this description, that the axle is affixed to the femoral component and received in an oversized, specially shaped hole in the post of the tibial component, the

, relative rotation requires a slight cocking of the femoral component relative to the tibial component which, in turn, means that the interengaging condylar portions of the two components, by reason of their shape in transverse cross-section, requires a small amount of vertical movement of the femur relative to the tibia;

2. There is a small clearance 1 between the axle of the anterior and posterior surfaces in the upper portion of the hole for the same reason as the clearance described in subparagraph 1 above. The desirable small rotational laxity in the prosthesis requires that the axle cock or rotate slightly in the hole in conjunction with the relative cocking or rotation of the femoral component relative to the tibial component. The magnitude of the anteriorposterior clearance increases to a maximum in the bottom portion of the hole and establishes the degree of rotational laxity with the leg in the various positions, since the degree of which the axle cocks in the hole is limited by engagement of the axle with the walls of the axle hole;

3. There is a relatively large clearance b between the bottom portion of the axle and the bottom portion of the hole to allow for relative downward displacement resulting from the variable dimension between the above-mentioned imaginary plane defined by the extremities of the femoral condylar portions of the femoral component and the axis AA of the axle.

By comparing FIGS. 1 and 6 of the drawings and, of course, in view of the variable dimension between the axis of the axle and the plane defined by extremities of the femoral condylar portions of the femoral component, it is evident that the axle 20 occupies a position near the top of the opening 40 when the leg is at maximum extension, occupies a position near the bottom of the opening when the leg is at full flexure and occupies variable intermediate positions between the top and bottom at various degrees of leg flexure. Inasmuch as the clearance in the anterior-posterior direction between the axle 20 and the opening 40 is greater in approximate proportion to the degree of flexure of the leg and inasmuch as the cocking of the axle in the opening 40 is limited by the clearance in the anterior-posterior direction, the hinge arrangement in the prosthesis provides a minimum amount of rotational laxity in the joint with the leg at full extension and increasing degrees of rotational laxity in approximate proportion to the degree of flexure of the leg.

Rotational laxity in the prosthesis is also afforded by providing geometrical and dimensional relationships between the slot 30 in the femoral component and the lateral faces of the post 38 of the tibial component that permit rotational laxity. Preferably, however, such relationships also restrict lateral laxity, i.e., relative translation in the lateral direction of the femoral and tibial components. The geometrical and dimensional relationships between the slot 30 and the post 38 in an exemplary embodiment of the prosthesis are best seen in FIG. 4 of the drawings.

The faces defining the slot 30 are planar and parallel and are spaced apart a distance designated S. The line XX in FIG. 4 represents a plane through the axle that is perpendicular to the major surface of the tibial component. The lines YY in FIG. 4 represents a plane through the axis of the axle opening in the post 38 and perpendicular to the major plane of the tibial component.

In cross section, along at least a portion that is received within the slot 30, the post 38 includes a center portion that is rectangular and has a dimension d approximately equal to the maximum dimension of the opening 40 and a dimension A that is somewhat less than the dimension S between the faces of the slot. The dimension A is chosen so that when the post 38 (and thus the tibial component) rotates or cocks relative to the femoral component in either direction through an angle equal to one-half or any other desired fraction of the total desired maximum rotation, the corners of the rectangular portion of the post 38 engage the faces of the slot 30.

The portions of the lateral faces of the post 38 outwardly from the cross-sectionally rectangular portion of the post converge outwardly, and the included angle between the planes of the convergent portions is equal to the desired amount of rotational laxity in the prosthesis. Accordingly, when the tibial component rotates relative to the femoral component to an extent equal to one-half or any other selected fraction in either direction, the convergent faces engage corresponding portions of the walls of the slot 30. FIG. 4 illustrates such engagement and therefore illustrates the manner in which the dimensional and geometrical relationships between the post and the slot limit the amount of maximum rotation of the tibial component relative to the femoral component.

It is evident from FIG. 4 and from appropriate trigonometric calculations of the dimensions and angles illustrated in FIG. 4 that only a relatively small lateral clearance between the lateral faces of the post 38 in the rectangular medial portion and the walls of the slot 30 (S minus A) is necessary to permit a substantial angular rotation. Accordingly, rotational laxity is afforded without introducing any substantial lateral laxity. Moreover, the matching shapes in transverse crosssection of the condylar surface of the femoral component and the condylar surface of the tibial component restricts, in any event, relative lateral translation.

The geometrical and dimensional relationships between the post and the slot described above and illustrated in FIG. 4 are merely exemplary. A similar result of providing rotational laxity in the prosthetic joint may be achieved by providing an appropriate clearance between a planar face or by providing outwardly convexly curved lateral faces on the post. Moreover, the crosssectional shapes of the walls of the slot may be altered, rather than or in addition to altering the cross-sectional shape of the post.

In addition to affording rotational laxity as well as controlling the degree of rotational laxity as a function of the degree of flexure of the leg, the construction of the hinge in the embodiment of the prosthesis shown in the drawings affords anterior-posterior laxity, which is also a characteristic of the anatomical knee joint. Thus, the prosthesis of the invention permits restoration of function in a manner reasonably duplicating the functions of the anatomical knee joint. Nonetheless, the prosthesis restores stability by controlling and limiting lateral, rotational and anterior-posterior laxity.

The above-described embodiments of the invention are intended to be merely exemplary, and those skilled in the art will be able to make numerous variations and modifications of them without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as defined in the appended claims.

I claim:

1. A knee joint prosthesis comprising a femoral eoma ponent having a pair of condylar portions laterally spaced-apart from each other and having outwardly facing surfaces generally matching in shape the anatomical surfaces of the femoral condyles (the condylar surfaces of the femur) and an intercondylar portion interconnecting the femoral condylar portions, the intercondylar portion being generally U-shaped and defining a slot located between the femoral condylar portions and adapted to open toward the tibial plateau; a tibial component in the form of a plate-like platform adapted to be positioned on the tibial plateau and having laterally spaced-apart outwardly facing condylar surfaces disposed opposite the femoral condylar portions of the femoral component for support thereof and a post extending upwardly into the slot in the femoral component; and an axle extending transversely across the slot in the femoral component through a hole in the post of the tibial component and into aligned holes in leg portions of the intercondylar portion on either side of the slot in the femoral component and connecting the tibia] and femoral components together in hinged relation for relative pivotal movement of the components about a transverse pivot axis to afford flexion of the leg at the joint, each hole into which the axle extends in at least one of the components of the prosthesis having a clearance from the axle in a selected zone, the clearance being shaped, dimensioned and positioned to afford relative rotation between the tibial and femoral components about an axis parallel to the axis of the tibia, i.e., to provide rotational laxity in the joint, the rotational laxity being at a maximum when the prosthesis is in a position corresponding generally to full leg flexion and the outwardly facing surfaces of the condylar portions of the femoral component are in contact with the outwardly facing condylar surfaces of the tibial component, the rotational laxity being at a minimum when the prosthesis is in a position corresponding to full leg extension and said surfaces are in contact.

2. A knee joint prosthesis according to claim 1 wherein there are clearances between lateral faces of the post of the tibial component and the faces of the intercondylar portion defining the slot in the femoral component.

3. A knee joint prosthesis according to claim 1 and further comprising a tibial pin extending through an opening in the tibial component and positioned in the component to extend through the tibial epiphysis.

4. A knee joint prosthesis according to claim 1 and further comprising a pin connected to the femoral component and positioned on the component to extend through the femoral epiphysis.

5. A knee joint prosthesis according to claim 4 wherein the pin of the femoral component is unitary with the intercondylar portion of the femoral component and is an extended curved portion of reduced transverse cross-section merging smoothly with the intercondylar portion of the femoral component.

6. A knee joint prosthesis according to claim 1 wherein each of the femoral condylar portions of the femoral component is an elongated doubly curved member shaped and dimensioned to extend from generally the anterior to generally the posterior of the femoral condyle and having (a) a varying curvature in the anterior-posterior direction closely matching the anatomical shape of the femoral condyle and (b) in transverse cross-sections along its length a laterally outwardly located essentially flat zone and a laterally inwardly located curved zone that is externally convex, and wherein each condylar surface of the tibial component has in transverse cross-section a shape matching the cross-sectional shape of the condylar surface of the corresponding femoral condylar portion of the femoral component.

7. A knee joint prosthesis according to claim 6 wherein each condylar surface of the tibial component is a surface generated by a substantially straight anterior-posterior line line moved along a path conforming substantially to the transverse shape of the corresponding condylar surface of the femoral condylar portions of the femoral component.

8. A knee joint prosthesis according to claim 1 wherein the axis of the axle is positioned to be spaced posteriorally from the axis of the tibia.

9. A knee joint prosthesis according to claim 1 wherein the distance between the axis of the axle and an imaginary surface matching the lateral profiles of the femoral condylar surfaces of the femoral component is at or near a maximum at the anterior extremity of such surface and generally diminishes at successive points on such surface moving from the anterior extremity toward the posterior extremity of such surface.

10. A knee joint prosthesis comprising a femoral component having a pin portion positioned on the femoral component to extend through the femoral epiphysis, a pair of laterally spaced-apart femoral condylar portions in the form of anteriorally-posteriorally elongated, doubly curved plate-like members having a vary- 'ing curvature in the anterior-posterior direction and having outwardly facing condylar surfaces generally matching the anatomical shapes of the respective condylar surfaces of the femoral condyles and an intercondylar portion connected to the inner edges of the respective femoral condylar portions and to the pin, the intercondylar portion having an outwardly open slot located generally between the femoral condylar portions of the femoral component and adapted to face the tibial plateau; a tibial component in the form ofa platelike platform adapted to be positioned on the tibial plateau and including in each of the laterally outward zones of the surfaces thereof facing the condylar surfaces of the femoral condylar portions of the femoral component a condylar surface positioned in facing relation to the corresponding condylar surface of the femoral component, each condylar surface of the tibial component having a shape closely matching intransverse cross-sections along its length the transverse shape of the corresponding condylar surface of the femoral component and being a surface generated by a generally straight anterior-posterior line moved along a path conforming to said transverse shape of said corresponding condylar surface of the femoral component, the tibial component further including a post projecting upwardly from the upper surface thereof and received in the slot in close clearance relation to the walls of the slot; means adapted for securing the tibial component to the tibia; and an axle coupling the tibial component and femoral component together in hinged relation for relative pivotal movement of the components about a transverse pivot axis to afford flexion of the leg at the joint, the axle extending through aligned transverse openings in the post of the tibial component and the intercondylar portion of the femoral component, each axle opening in at least one of the components having, with the leg at or near full extension, the following clearance relationships with the axle;

l. a clearance in the anterior-posterior direction to afford relative rotation between the tibial and femoral components about an axis parallel to the axis of the tibia, i.e., to provide rotational and anteriorposterior translational laxity in the joint, the rotational laxity being at a minimum when the leg is at or near full extension and the outwardly facing condylar surfaces of the condylar portions of the femoral component are in contact with the condylar surfaces of the tibial component, the rotational laxity being at a maximum when the leg is at or near full flexion and said surfaces are in contact;

2. a very small clearance between the top of the axle and the top of the opening to afford a slight upward displacement of the femoral component in a direction away from the tibial component in conjunction with the relative rotation between the components about an axis parallel to the axis of the tibia;

3. a clearance between the lower portion of the axle and the lower portion of the opening to enable angular displacement of the femoral component in an anterior-posterior direction relative to the tibial component upon flexion of the joint, i.e., flexural laxity.

11. A knee joint prosthesis according to claim 10 wherein the axis of the axle is positioned to be spaced posteriorally from the axis of the tibia and the distance between the axis of the axle and an imaginary surface defined by the extremities of the condylar surfaces of the femoral condylar portions of the femoral component is at or near maximum at the anterior extremity of said imaginary surface and generally diminished at successive points moving from the anterior extremity toward the posterior extremity and wherein the axle engages .the top of the opening when the leg reaches full extension so that flexion substantially beyond full extension is precluded.

12. A knee joint prosthesis according to claim 10, wherein there is a clearance of outwardly increasing magnitude between the surfaces defining the slot in the intercondylar portion of the femoral component and the lateral faces of the tibial post, moving along an anterior-posterior axis in at least one direction from the zone of a plane parallel to the axis of the tibia and including the axis of the axle.

13. A knee prosthesis according to claim 12 wherein the surfaces defining the slot in the femoral component are planar and parallel and are positioned on the femoral component to be oriented substantially anteriorally posteriorally of the femur and wherein portions of the lateral faces of the tibial post on at least one side of said plane converge outwardly.

14. A knee joint prosthesis according to claim 13 wherein said portions of the lateral faces of the tibial post are planar and the planes thereof intersect at an angle equal to the desired maximum degree of rotational laxity permitted by the prothesis.

15. A knee joint prosthesis according to claim 14 wherein said angle is on the order of 12.

16. A knee joint prosthesis according to claim 10 wherein the axle is affixed to the intercondylar portion of the femoral component and all clearances are between the axle and the opening in the tibial post, the opening in the post, as viewed axially, being defined by a substantially arcuate upper wall in relatively closer clearance with the axle, a substantially arcuate lower wall in relatively larger clearance with the axle, and substantially straight side walls connecting and merging smoothly with the upper and lower walls, whereby the rotational laxity afforded by the prosthesis is at a maximum when the axle resides in the power portion of the opening (its position at full leg flexion) and is at a minimum when the axle resides in the upper portion of the opening (its position at full leg extension).

17. A knee joint prosthesis according to claim wherein the under surface of the tibial component has at least one slot therein for enhancing the fixation of the tibial component to the tibia against movement out of its position as placed.

18. A knee joint prosthesis according to claim 10 wherein the tibial component has a recess at the medial anterior portion of the upper surface thereof and where the tibial pin includes an enlarged head portion received in said recess.

19. A knee joint prosthesis according to claim 10, wherein the under surface of the tibial component has at least one boss projecting therefrom for enhancing the fixation of the tibial component to the tibia against movement out of its position as placed.

@1 53? STATES PATEm Gm:

CERTIFICATE OF Patent 3,8-37,009 Da September 24, 1974 r Inventor(s) Peter S. Walker It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column '1, line '13, "an" should read --and--; Column '2', line "1, "surfaces" should read -surface; Column 2', line "anteriorally posteriorally" should read nteriorally-posteriorally-; Column 2, lin'esi 22""a'nd 23 "doubly curved" should read --doublycurved"; Column 2', line 33, "anteriorally posteriorally" should read anteriorally-posteriorally-; Column 2, line-p52 "anteriorally posteriorally" should read anteriorallyposteriorally-; Column '2, line '59-, "component" should read -components--; Column '5, line 33 f after "lock" insert a comma; Column '7', line '31-, "for" should read -from-; Column '8, line 6, "of" should read -and-; column 8, line 1-7, "of" should read --to-; n i Column '8', 'lin'ef62, "represents" should read "represent"; Column 11', line 13',- delete "line" (second occurrence); Column 12', line 22, "the relative" should read --a relative-"'7 Column 12', l'i n'e Z; ;"d iminished" should read --diminishes-; and Column 1 2', lines 54-55 "anteriorally posteriorally" should read -anteriorally-posteriorally--'.

Signed and sealed this 28th day of January I975.

(SEAL) Attest: i

McCOY M. GIBSON JR. C. MARSHALL DANN Attescing Officer Commissioner of Patents 

1. A knee joint prosthesis comprising a femoral component having a pair of condylar portions laterally spaced-apart from each other and having outwardly facing surfaces generally matching in shape the anatomical surfaces of the femoral condyles (the condylar surfaces of the femur) and an intercondylar portion interconnecting the femoral condylar portions, the intercondylar portion being generally U-shaped and defining a slot located between the femoral condylar portions and adapted to open toward the tibial plateau; a tibial component in the form of a platelike platform adapted to be positioned on the tibial plateau and having laterally spaced-apart outwardly facing condylar surfaces disposed opposite the femoral condylar portions of the femoral component for support thereof and a post extending upwardly into the slot in the femoral component; and an axle extending transversely across the slot in the femoral component through a hole in the post of the tibial component and into aligned holes in leg portions of the intercondylar portion on either side of the slot in the femoral component and connecting the tibial and femoral components together in hinged relation for relative pivotal movement of the components about a transverse pivot axis to afford flexion of the leg at the joint, each hole into which the axle extends in at least one of the components of the prosthesis having a clearance from the axle in a selected zone, the clearance being shaped, dimensioned and positioned to afford relative rotation between the tibial and femoral components about an axis parallel to the axis of the tibia, i.e., to provide rotational laxity in the joint, the rotational laxity being at a maximum when the prosthesis is in a position corresponding generally to full leg flexion and the outwardly facing surfaces of the condylar portions of the femoral component are in contact with the outwardly facing condylar surfaces of the tibial component, the rotational laxity being at a minimum when the prosthesis is in a position corresponding to full leg extension and said surfaces are in contact.
 2. A knee joint prosthesis according to claim 1 wherein there are clearances between lateral faces of the post of the tibial component and the faces of the intercondylar portion defining the slot in the femoral component.
 2. a very small clearance between the top of the axle and the top of the opening to afford a slight upward displacement of the femoral component in a direction away from the tibial component in conjunction with the relative rotation between the components about an axis parallel to the axis of the tibia;
 3. a clearance between the lower portion of the axle and the lower portion of the opening to enable angular displacement of the femoral component in an anterior-posterior direction relative to the tibial component upon flexion of the joint, i.e., flexural laxity.
 3. A knee joint prosthesis according to claim 1 and further comprising a tibial pin extending through an opening in the tibial component and positioned in the component to extend through the tibial epiphysis.
 4. A knee joint prosthesis according to claim 1 and further comprising a pin connected to the femoral component and positioned on the component to extend through the femoral epiphysis.
 5. A knee joint prosthesis according to claim 4 wherein the pin of the femoral component is unitary with the intercondylar portion of the femoral component and is an extended curved portion of reduced transverse crOss-section merging smoothly with the intercondylar portion of the femoral component.
 6. A knee joint prosthesis according to claim 1 wherein each of the femoral condylar portions of the femoral component is an elongated doubly curved member shaped and dimensioned to extend from generally the anterior to generally the posterior of the femoral condyle and having (a) a varying curvature in the anterior-posterior direction closely matching the anatomical shape of the femoral condyle and (b) in transverse cross-sections along its length a laterally outwardly located essentially flat zone and a laterally inwardly located curved zone that is externally convex, and wherein each condylar surface of the tibial component has in transverse cross-section a shape matching the cross-sectional shape of the condylar surface of the corresponding femoral condylar portion of the femoral component.
 7. A knee joint prosthesis according to claim 6 wherein each condylar surface of the tibial component is a surface generated by a substantially straight anterior-posterior line line moved along a path conforming substantially to the transverse shape of the corresponding condylar surface of the femoral condylar portions of the femoral component.
 8. A knee joint prosthesis according to claim 1 wherein the axis of the axle is positioned to be spaced posteriorally from the axis of the tibia.
 9. A knee joint prosthesis according to claim 1 wherein the distance between the axis of the axle and an imaginary surface matching the lateral profiles of the femoral condylar surfaces of the femoral component is at or near a maximum at the anterior extremity of such surface and generally diminishes at successive points on such surface moving from the anterior extremity toward the posterior extremity of such surface.
 10. A knee joint prosthesis comprising a femoral component having a pin portion positioned on the femoral component to extend through the femoral epiphysis, a pair of laterally spaced-apart femoral condylar portions in the form of anteriorally-posteriorally elongated, doubly curved plate-like members having a varying curvature in the anterior-posterior direction and having outwardly facing condylar surfaces generally matching the anatomical shapes of the respective condylar surfaces of the femoral condyles and an intercondylar portion connected to the inner edges of the respective femoral condylar portions and to the pin, the intercondylar portion having an outwardly open slot located generally between the femoral condylar portions of the femoral component and adapted to face the tibial plateau; a tibial component in the form of a plate-like platform adapted to be positioned on the tibial plateau and including in each of the laterally outward zones of the surfaces thereof facing the condylar surfaces of the femoral condylar portions of the femoral component a condylar surface positioned in facing relation to the corresponding condylar surface of the femoral component, each condylar surface of the tibial component having a shape closely matching in transverse cross-sections along its length the transverse shape of the corresponding condylar surface of the femoral component and being a surface generated by a generally straight anterior-posterior line moved along a path conforming to said transverse shape of said corresponding condylar surface of the femoral component, the tibial component further including a post projecting upwardly from the upper surface thereof and received in the slot in close clearance relation to the walls of the slot; means adapted for securing the tibial component to the tibia; and an axle coupling the tibial component and femoral component together in hinged relation for relative pivotal movement of the components about a transverse pivot axis to afford flexion of the leg at the joint, the axle extending through aligned transverse openings in the post of the tibial component and the intercondylar portion of the femoral component, each axle opening in at least one of tHe components having, with the leg at or near full extension, the following clearance relationships with the axle;
 11. A knee joint prosthesis according to claim 10 wherein the axis of the axle is positioned to be spaced posteriorally from the axis of the tibia and the distance between the axis of the axle and an imaginary surface defined by the extremities of the condylar surfaces of the femoral condylar portions of the femoral component is at or near maximum at the anterior extremity of said imaginary surface and generally diminished at successive points moving from the anterior extremity toward the posterior extremity and wherein the axle engages the top of the opening when the leg reaches full extension so that flexion substantially beyond full extension is precluded.
 12. A knee joint prosthesis according to claim 10, wherein there is a clearance of outwardly increasing magnitude between the surfaces defining the slot in the intercondylar portion of the femoral component and the lateral faces of the tibial post, moving along an anterior-posterior axis in at least one direction from the zone of a plane parallel to the axis of the tibia and including the axis of the axle.
 13. A knee prosthesis according to claim 12 wherein the surfaces defining the slot in the femoral component are planar and parallel and are positioned on the femoral component to be oriented substantially anteriorally posteriorally of the femur and wherein portions of the lateral faces of the tibial post on at least one side of said plane converge outwardly.
 14. A knee joint prosthesis according to claim 13 wherein said portions of the lateral faces of the tibial post are planar and the planes thereof intersect at an angle equal to the desired maximum degree of rotational laxity permitted by the prothesis.
 15. A knee joint prosthesis according to claim 14 wherein said angle is on the order of 12*.
 16. A knee joint prosthesis according to claim 10 wherein the axle is affixed to the intercondylar portion of the femoral component and all clearances are between the axle and the opening in the tibial post, the opening in the post, as viewed axially, being defined by a substantially arcuate upper wall in relatively closer clearance with the axle, a substantially arcuate lower wall in relatively larger clearance with the axle, and substantially straight side walls connecting and merging smoothly with the upper and lower walls, whereby the rotational laxity afforded by the prosthesis is at a maximum when the axle resides in the power portion of the opening (its position at full leg flexion) and is at a minimum when the axle resides in the upper portion of the opening (its position at full leg extension).
 17. A knee joint prosthesis according to claim 10 wherein the under surface of the tibial compoNent has at least one slot therein for enhancing the fixation of the tibial component to the tibia against movement out of its position as placed.
 18. A knee joint prosthesis according to claim 10 wherein the tibial component has a recess at the medial anterior portion of the upper surface thereof and where the tibial pin includes an enlarged head portion received in said recess.
 19. A knee joint prosthesis according to claim 10, wherein the under surface of the tibial component has at least one boss projecting therefrom for enhancing the fixation of the tibial component to the tibia against movement out of its position as placed. 